Biology (from Greek: βίος, bio, "life"; and λόγος, logos, "speech") is the branch of science that studies life, including the origin, distribution, structure, and function of living organisms, as well as their classification. Biology evolved out of other natural sciences and medicine as a discipline of its own in the mid to late 19th century. Along with chemistry and physics it is now one of the three sciences that are commonly taught in schools.

Biological research underpins most of modern medicine. The knowledge of how enzymes and cells work is essential for the production of effective drugs. Biologists also study bacteria and viruses which cause illness and most importantly, can track what can and cannot kill them.

Biology also underpins evolutionary theory. Genetics and the study of DNA falls under biology as well as the tracking of evolutionary changes in species. Evolution is an important underlying principle of modern biology and is the basis for knowing where biological processes came from and how they will react to different stimuli.